Technical Field
Disclosed is a liquid crystal panel including optically anisotropic elements between a liquid crystal cell and a polarizer. A liquid crystal display including the liquid crystal panel is also disclosed.
Description of Related Art
A liquid crystal panel includes a liquid crystal cell between a pair of polarizers. In an in-plane switching (IPS) mode liquid crystal cell, liquid crystal molecules are homogeneously aligned in a direction substantially parallel to a substrate surface in a non-electric-field state, and by application of an electric field in a horizontal direction, the liquid crystal molecules are rotated in a plane parallel to the substrate surface to control right transmission (white image display) and shielding (black image display). A horizontal electric field type liquid crystal panel including liquid crystal molecules homogeneously aligned in a non-electric-field state, e.g., an IPS mode liquid crystal panel, has a small color shift in neutral colors, and is thus excellent in viewing angle characteristics.
However, when an IPS mode liquid crystal panel is viewed from an oblique direction at an angle of 45 degrees (azimuth angle of 45 degrees, 135 degrees, 225 degrees or 315 degrees) with respect to the absorption axis of a polarizer, light leakage in black image display is significant, so that a color shift and a reduction in contrast easily occur. Accordingly, a method has been proposed in which an optically anisotropic element (retarder) is disposed between a liquid crystal cell and a polarizer for the purpose of reducing a color shift and improving a contrast in an oblique viewing direction.
For example, JP 2005-208356 A describes a method for reducing black luminance and color shift of an IPS mode liquid crystal panel in an oblique direction with using a plurality of optically anisotropic elements. Reduction of black luminance and color shift in a direction at azimuth angle of 45° and polar angle (angle with respect to the normal direction of a panel surface) of 60° is explained with using a Poincare sphere. WO 2008/156011 proposes a method in which color shift in a direction at azimuth angle of 45 degrees in an IPS mode liquid crystal panel is reduced by combining an optically anisotropic element having a refractive index anisotropy of nz≧nx>ny (negative-A plate or positive-B plate) and an optically anisotropic element having a refractive index anisotropy of nx>ny>nz (negative-B plate).
By disposing a plurality of optically anisotropic elements between a liquid crystal cell and a polarizer as described above, contrast and color shift in an oblique direction can be improved. However, when optical designing is performed in such a manner that a contrast at a specific angle, e.g., azimuth angle of 45° and polar angle of 60°, becomes the maximum, light leakage (black luminance) at other angles may increase. Accordingly, for reducing the black luminance in every direction to enhance visibility, further improvement is needed. In WO2008/156011, optical designing is performed so as to reduce the color shift in a direction at an azimuthal angle of 45°, but the contrast is not sufficiently improved.
Thus, in conventional configurations, studies on improvement of visibility by enhancing the contrast in every direction have not been necessarily sufficiently done, and there is room for improvement. In view of such circumstances, an object of the present invention is to provide a liquid crystal panel and a liquid crystal display which exhibit a high contrast when viewed at any angle in an oblique direction and which have further improved visibility.